I need to know this to understand more about LibreOffice Writer configuration.
That should be helpful: 
Complex Text Layout (CTL) 
Complex Text Layout - Options 
Languages Using Complex Text Layout 
You might also find something on this topic in Asian languages:
https://ask.libreoffice.org/
So I should always enable Asian language too when my document is in Thai, shouldn’t I?

No. Enabling Complex Text Layout (CTL) is sufficient.
           
           
           1 Like
         
         